C. CAUSA EFFICIENS We shall not be led away from Aristotle's clear presentation of the efficient cause ('What initiated a motion') by any of these variations and reductions: (1) Reduction of it to the formal cause in the manner of Platonists, so that the form or pattern of an emotion is said to be the power, force or agency that sets the emotion going. (2) Reduction of it to the final cause in the manner of Leibniz, which would mean that the final outcome or purpose of an emotion initiates the emotion. (3) Reduction of it to the material cause in the manner of Marxists, which would endow the material stuff of emotion with the power of self-activation. (4) Nor do we accept that the efficient cause is really extrinsic or secondary (Occasionalism), a mere instrument in some hidden plan of a prime mover, because the problem of efficient causality, or 'what initiated a motion', remains. (5) Neither do we admit the scepticism of Hume who finds that efficient causality cannot be demonstrated. We have already dealt with the issue of demonstration above. Because Hume's position led to the corollary position (Kant) that causality must-because it is undemonstrable-be an a priori category of the mind, modern science finds the concept too subjective, too anthropomorphic. It prefers to state the problems of cause-and-effect in terms of laws or functions, or what are called 'if-then' statements. Whether or not efficient causality is demonstrable, whether or not it is restated in conditional language or in the form of probability curves, it remains one fundamental answer to the question 'why'.